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Tiny but troublesome

We need to have a varied mix of animals and plants at the school farm, but this can leave us trying to keep an eye on many things.

White fly on the underside of a butternut squash leaf

The last month has seen fine warm weather – it’s often been hot inside the poly tunnels. I checked the tunnels two weeks ago and noticed tiny white flies on the leaves of both the tomatoes and the squashes. They are, unsurprisingly, called ‘whitefly‘ and are a pest of crops in both greenhouse and poly tunnels, and they like warmth. Within a few weeks, if the conditions are right, there can be thousands of them – the conditions have been right and there are thousands of them! White fly larvae damage crops rather like aphids do – they suck the plants sap and that weakens, even dries out, the plant. As you can see none of the plants look perfectly healthy. Weak plant then are vulnerable to other diseases and problems, ours now have sooty molds growing where white fly has caused damage.

Encarsia wasp pupae can just be seen in the black blob on the card

There are options for dealing with white fly, either chemical spray or biological control. We don’t like to use chemical spray, so I turned to biological controls.

White flies are white and tiny. But even they have their own pests – tiny little (harmless) parasitic wasps called ‘Encarsia formosa‘ – they’re so small they’re hard to see. You can buy these wasp, which come on a little card that you hang in the plants with the wasp ready to hatch on them. The wasps hatch within a few days and seek out white fly larvae, they then lay their eggs on the white fly larvae and the wasp larvae eat them. Great! But, it takes time for that to happen and, this year, the damage to our plants may well be done.

Tiny Encarsia wasps just hatched – about 1mm long.

Tomato leaf plastered in white fly scales

But, we’ve learnt a lesson and next year will be introducing the wasps before the white fly get out of control! The last picture shows how out of control they have got, a leaf covered in white fly scales ready to hatch…